In a magnetic recording system, the tracks on a magnetic recording disk comprise “read” sectors with “servo” sectors embedded between the read sectors. The servo sector typically begins with a known preamble pattern, followed by a Servo Address Mark (SAM) and various servo data. The Servo Address Mark is used to position a magnetic recording head over the magnetic recording disk so that the user information stored in the read sectors can be retrieved properly. The Servo Address Mark is typically detected using a Hamming detector or a Euclidean detector. Hamming detectors analyze a Hamming distance metric to detect the Servo Address Mark while Euclidean detectors analyze a Euclidean distance to detect the Servo Address Mark.
A Euclidean detector is generally considered to offer better performance than a Hamming detector due to a detection threshold Dthr that is adapted to obtain an optimum value. The adaptation of the detection threshold Dthr, however, requires that the Servo Address Mark is found. If the detection threshold Dthr is set improperly so that the Servo Address Mark is not found, then the adaptation will never converge.
A need therefore exists for improved teclmiques for adapting the detection threshold Dthr in Euclidean SAM detectors.